Today has been a great day for me thus far. For the current site I am working on, the client requested two features recently:

1) Allow him to reposition images(order)

2) Allow him to upload files and have his clients view/download them

Cool. Had no idea how to do either off the top of my head. Let’s try to tackle the first one.

On a high level, I was thinking this process should go something like this:

• See if an object had been updated
• Find out which object that was
• See the new position is has and if that position is already taken up
• Track whether that object went up or down in position
• Change the other positions accordingly

Myself and Avi were actually constructing the code to write this whole thing out. We started by writing a rails test:

Here we are testing to see if we change the position of a studio, we need the other studios’ positions to change accordingly.

Now here’s the real issue, all of the CRUD of an object in this app is being done by Active Admin. Actually I guess it wasn’t so hard to know where to look to solve this problem…callbacks.

Cool we here the best this to do is the have a before_save callback. We need to check if the current object has been changed. But wait, duh, there’s this thing called acts_as_list that does the reordering for you. Luckily, this gem has a method (:insert_at(#)) that not only inserts the object where you want it but also reorders the list, doing the heavy lifting for us.

Great. The idea that this process requires a before_save callback is right, and now we just need to connect the dots. We must ask if a object has been changed, then insert it accordingly:

and bam, we can change any object to have a different position and the rest of the positions are reordered, and it works with Active Admin. Check.